SENSATION AND PERCEPTION
AP Psychology
Sensation
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The process by which our sensory receptors and
nervous system receive and represent stimulus
energies from our environment.
Perception
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The process of organizing and interpreting sensory
information, enabling us to recognize meaningful
objects and events.
Bottom-up Processing
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Starts with sensory receptors and works up to the
brain’s integration of sensory information.
Top-down Processing
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Information processing guided by higher-level
mental processes, as when we construct perceptions
drawing on our experience and expectations.
Selective Attention
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Your conscious awareness focuses, like a flashlight beam, on only a very limited aspect of all you
experience
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Almost 80% of vehicle accidents involve driver distraction.
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The focusing of conscious awareness on a particular
stimulus.
Selective Inattention or Inattentional Blindness
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Failing to see visible objects when our attention is directed elsewhere
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Gorilla Experiment
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JabbaWockeez Experiment
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http://youtu.be/Yu3zlWVCcjY
Change Blindness
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Failing to notice changes in the environment
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http://youtu.be/Yu3zlWVCcjY (JabbaWockeez)
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http://youtu.be/vJG698U2Mvo
Absolute Threshold
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The minimum stimulation needed to detect a particular stimulus 50 percent of the time.
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The mosquito ring tone
Ring Tone
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http://www.youtube.com/watch?v=IrewnzQYrPI
Difference Thresholds or
“Just Noticeable Difference”
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The minimum difference a person can detect between any two stimuli half the time.
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The detectable difference increases with the size of the stimulus
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Weber’s Law – Principle that to be perceived as
different, two stimuli must differ by a constant
percentage (rather than a constant amount.)
TWO LIGHTS MUST DIFFER BY 8%
TWO OBJECTS MUST DIFFER IN WEIGHT BY 2%
TWO TONES MUST DIFFER
.3%
Subliminal
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Below one’s absolute threshold for conscious awareness.
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ABT = 50% of the time … at or slightly below the threshold, we still detect the stimulus some of the time (subliminal)
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Overall, subliminal messages do not have a
powerful, enduring effect on behavior.
Priming
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The activation, often unconsciously, of certain associations, thus predisposing one’s perception, memory, or response.
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Rat/Man experiment
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An invisible image or word can briefly prime your
response to a later question.
Signal Detection Theory
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A theory predicting how and when we detect the presence of a faint stimulation (signal) amid
background stimulation (noise).
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Assumes there is no single absolute threshold and that detection depends partly on a person’s
experience, expectations, motivation, and alertness.
Sensory Adaptation AKA. Habituation
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Diminished sensitivity as a consequence of constant stimulation.
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Smelly Perfume …
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A ticking clock …
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What is the function of sensory adaptation?
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Allows our attention to focus on changing stimuli.
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We perceive the world not exactly as it is, but as it is
useful for us to perceive it.
National Geographic Brain Games
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http://www.youtube.com/watch?v=ueodBZGpCL0
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22 minute version
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http://www.youtube.com/watch?v=d0W60BX_6wA
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7 minute version
VISION
Transduction
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The conversion of one form of energy into another.
In sensation, the transforming of stimulus energies, such as sights, sounds, and smells, into neural
impulses our brains can interpret
OUR EYE RECEIVES LIGHT ENERGY AND
TRANDUCES
(TRANSFORMS) IT INTO NEURAL MESSAGES THAT
OUR BRAIN THEN
PROCESSES INTO WHAT
WE CONSCIOUSLY SEE.
Sight
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What strikes our eyes is not color but pulses of
electromagnetic energy that our visual system
perceives as color.
Light’s Physical Characteristics
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Wavelength – the distance from one wave peak to the next determines its hue (the color we
experience, such as blue or green)
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Intensity – the amount of energy in light waves
(amplitude, or height) influences brightness
How We See
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1. Light enters eye through the cornea which
protects the eye and bends light to provide focus.
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2. The light then passes through the pupil ( a small adjustable opening surrounded by the iris)
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3. The iris = a colored muscle that adjusts light intake. Dilates and constricts in response to light intensity and emotion.
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Iris scanning machines
How We See
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4. Behind the pupil is the lens = focuses incoming light rays into an image on the retina.
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5. The retina = a multilayered tissue on the eyeball’s sensitive inner surface.
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The lens focuses the rays by changing its curvature in a process called accommodation.
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The retina doesn’t see a whole image. Rather, its
millions of receptor cells convert the particles of light
energy into neural impulses and forward those to the
brain. In the brain, the impulses are reassembled into a
perceived and upright-seeing image.
The Retina – Rods and Cones
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Outer Layer - Photoreceptors
◼ Rods – retinal receptors that detect black, white, and gray;
necessary for peripheral and twilight vision, when cones do not respond
◼ Cones – retinal receptors that are concentrated near the center of the retina. Function in daylight and well-lit conditions. Detect fine detail and give rise to color sensations.
◼ Light energy trigger chemical changes that would spark neural signals, activating bipolar cells. The bipolar cells in turn would activate ganglion cells
Retina and Fovea
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Fovea = the central focal point in the retina, around which the eye’s cones cluster.
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Rods predominate around the peripheral of the fovea.
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Cones = detail
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Rods = faint light
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Some animals like toads, mice, and rats have retinas
made up entirely of rods, allowing them to function in
dim light … but probably have poor color vision.
Retina and the Optic Nerve
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Axons from the neural network of ganglion cells converge, like strands of a rope, to form the optic nerve.
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The optic nerve carries information to your brain.
(Where the thalamus will receive and distribute the information.)
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The optic nerve can seen nearly 1 million messages
at once through its nearly 1 million ganglion fibers.
Optic Nerve and Blind Spot page 127
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Where the optic nerve leaves the eye there are no receptor cells – creating a blind spot.
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Without seeking your approval – your brain fills in
the hole.
Retina
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After processing by your retina’s 130 million receptor rods and cones,
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information travels to your bipolar cells,
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then to your millions of ganglion cells,
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through their axons making up the optic nerve,
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These axons run to the thalamus
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Where the synapse with neurons that run to the
visual cortex in the occipital lobe
Retina
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Your retinal cells are so responsive that even
pressure triggers them. But your brain interprets their firing as light.
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Close your eyes … turn your eyes to the left … then gently rub the right side of your right eyelid with your finger tip.
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What do you see?
Feature Detection
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Feature detection cells respond to a scene’s specific features – to particular edges, lines, angles, and
movements.
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Feature detector cells in the visual cortex pass such
information to other cortical areas.
Parallel Processing
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The brain divides a visual scene into subdimensions:
such as color, movement, form, and depth.
HOW DO WE SEE COLOR?
Young-Helmholtz Trichromatic (three color) theory
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The retina contains three different color receptors.
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One most sensitive to red, one to green, one to blue.
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When stimulated in combinations – we see a variety
of color.
Opponent-Process Theory
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Opposing Retinal processes (red-green, yellow-blue, white-black) enable color vision.
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For example, some cells are stimulated by green and inhibited by red; others are stimulated by red an
inhibited by green.
Processing Color
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TWO STAGES
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1. The retina’s red, green, and blue colors respond to varying degrees to different color stimuli
(Helmholtz’s theory)
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2. Their signals are then processed by the nervous
system’s opponent process cells, en route to the
visual cortex.
HEARING
Sound Waves
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Frequency determines pitch
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(long waves = low frequency = low pitch)
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short waves = high frequency = high pitch)
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Amplitude determines loudness
CONVERTING WAVES TO
SOUND
The Outer Ear
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Outer Ear – channels sound through the auditory canal to the …
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Ear Drum ( a tight membrane that vibrates with the
waves)
The Middle Ear
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The middle ear then transmits the eardrum’s
vibrations through a piston made of three tiny bones
…
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(The hammer, the anvil, and stirrup)
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To the ….
Inner Ear
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The Cochlea – snail shaped tube in the inner ear.
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The incoming vibrations cause the cochlea’s membrane (the oval window) to vibrate, jostling the fluid that fills the tube.
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This motion cause ripples in the basilar membrane, bending the hair cells lining its surface.
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Hair cell movement triggers impulses in the adjacent nerve cells, whose axons converge to form the auditory
nerve, which sends neural messages (via the thalamus)to the temporal lobe’s auditory cortex.
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Also … Vestibular sense (sense of body movement, position, and balance. Semicirculuar canals and
vestibular sacs are filled with fluid and connect to the
cochlea.
Inner Ear
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Vestibular Sense
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Sense of body movement, position, and balance.
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Semicircular canals and vestibular sacs are filled with fluid and connect to the cochlea
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Send messages to the cerebellum
FROM VIBRATION AIR TO MOVING PISTON TO FLUID
WAVES TO ELECTRICAL IMPUSLSES TO THE BRAIN
…. WE HEAR!
Sound
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Loudness – number of activated hair cells
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